1. Field of the Invention
This invention relates to an optical scanning system which is provided on a digital copier, e.g., laser printer or laser facsimile etc.
2. Description of the Related Art
A digital copier, e.g., laser printer or laser facsimile etc., has an optical scanning system including a latent image writing member which converges light on a photoconductive member (a photoconductive drum). An optical scanning lens converges the light via a polygonal mirror after light from a light source is coupled by a coupling lens (or a condenser lens). In this application, the word "couple" is interchangeable with words like "collimate" and "condense" etc.
However, in the conventional optical scanning system, a beam spot on the photoconductive member generates a corresponding Gaussian intensity distribution. The reason is that, in the case where a semiconductor laser or a gas laser is used as a light source, light flux, which is diffused from the light source, includes the Gaussian intensity distribution and is focused (via an optical scanning system which has a relatively small aberration) on the photoconductive member. Therefore, the beam spot has the Gaussian intensity distribution at a focus position on the photoconductive member.
If a beam spot should include the Gaussian intensity distribution when the beam spot is scanned in the optical scanning system and a latent image is written on the photoconductive member, a size of the latent image changes because of a dispersion of a lighting output from the light source or light sensitivity characteristics. Therefore, the output becomes a blurred image. This problem is an especially difficult obstacle to overcome when a high density image is realized.